With champagne spraying and music blasting, Alex Rodriguez smiled wide and laughed last night, sharing a moment with a dancing Eduardo Nunez and Ivan Nova in the Yankees’ clubhouse. Then he vanished into a back area of the clubhouse, not to be seen again.

Tonight, we’ll find out exactly how often we’ll be seeing him for the duration of this postseason run.

Behind the brilliant pitching of CC Sabathia, the Yankees withstood the challenge of the resilient Orioles, prevailing in the winner-take-all, loser-go-home American League Division Series Game 5 by a 3-1 margin. It felt like the end of a horror film, with the bloodied and exhausted Yankees barely standing after enduring 23 hard-fought games — regular season and postseason — with their new nemeses.

And like any horror-film survivors, the Yankees sustained their share of casualties. Their happiness over advancing to the AL Championship Series against Detroit, with Game 1 tonight in the Bronx, will immediately be qualified by this question:

“I’ll have a lineup for you tomorrow,” manager Joe Girardi said last night.

It seems pretty simple here: Either you give Rodriguez a fresh start and play him tonight against Tigers right-hander Doug Fister (Detroit’s unannounced but likely starter), or you keep him on the bench all the way through this round.

Rodriguez served as a mere observer in this clinching game, his first postseason benching since the 1995 Mariners deployed him, then 20 years old, as a reserve. Eric Chavez started at third base, going hitless in three at-bats, while Raul Ibanez — who pinch-hit memorably for A-Rod in Game 3 — started at designated hitter and broke a scoreless tie with a fifth-inning single, bringing home Mark Teixeira from second base.

When Baltimore manager Buck Showalter went to lefty reliever Troy Patton to go after Ibanez with two outs in the sixth inning, it seemed an open invitation for Girardi to bring in Rodriguez for the platoon advantage. Girardi passed, and Ibanez struck out to end the inning.

We know that Rodriguez hit righties terribly (.256 batting average, .326 on-base percentage and .391 slugging percentage) during the regular season, and has been far worse (0-for-14 with 11 strikeouts) in the just-completed ALDS. He looked better against Baltimore lefty starters Wei-Yin Chen and Joe Saunders, and in the regular season posted respectable numbers of .308/.410./514 against southpaws.

The problem arrives when you look at the Tigers’ pitching staff: Their starting rotation is 100 percent right-handed, with Anibal Sanchez, Justin Verlander and Max Scherzer likely to follow Fister. Rodriguez is a combined 2-for-24 lifetime against Fister, Sanchez and Scherzer and a pretty good 8-for-30 with three homers and six walks against the ace Verlander.

If Girardi continues to draw a hard line with Rodriguez, as he did the final three games of the ALDS — pinch-hitting for him twice before benching him outright — then Rodriguez wouldn’t start at all. He would basically be held in reserve each game as a pinch-hitter against Detroit’s two lefty relievers, former Yankee Phil Coke and Drew Smyly.

“It is what it is,” Rodriguez said yesterday, before the game. “I can’t control that. The only thing I can do is go out and try to have quality at-bats and help the team win.”

Could he rediscover even a scintilla of competence against righty pitching? It isn’t impossible. The guy has accomplished some things in his career, after all.

“He’s going to be big for us in this postseason,” Ibanez vowed.

But the time to ask that question is tonight, when you have the most room for error. When it’s 0-0, and even a Game 1 loss in the best-of-seven format wouldn’t dramatically set back the Yankees.

We’ll continue to wonder about Rodriguez’s long-term future with the Yankees. The fact he has five years remaining, with $114 million still to come in paychecks, is mind-blowing.

One crisis at a time, however. First, the Yankees have to determine how to use A-Rod against Detroit. The time to decide, the trend-setter and message-sender for the rest of this postseason, is tonight.